1. Field of the Invention
The present invention relates to a substrate having colored layers of different colors formed thereon, including colorless regions that are substantially colorless, and a method for producing the same. The substrate having colored layers of the present invention may be used in a reflective color liquid crystal display device that operates in a reflection display mode by reflecting incident light from the environment (hereinafter referred to also as xe2x80x9cambient lightxe2x80x9d), or in a transflective (hereinafter referred to also as xe2x80x9csemi-transmissivexe2x80x9d) color liquid crystal display device that operates in a reflection display mode under bright environments while operating in a transmission display mode by transmitting light from the backlight under dark environments.
2. Description of the Background Art
A semi-transmissive color liquid crystal display device is widely used as a display of a portable device, etc., as it is capable of operating in a reflection display mode using ambient light under bright environments, thereby reducing the power consumption, while operating in a transmission display mode using the backlight under dark environments, thereby making it possible to use the device under any environment.
A conventional semi-transmissive color liquid crystal display device is a two-way display type liquid crystal display device as disclosed in Japanese Laid-Open Patent Publication No. 11-183892. The publication discloses a liquid crystal display device in which openings are provided in red, green and blue color filters (hereinafter referred to also as xe2x80x9cCFsxe2x80x9d) provided on the inner surface of a front-side substrate so that each opening partially corresponds to a pixel region, with a reflection film being provided on the inner surface of a back-side substrate so as to correspond to the opening. When the liquid crystal display device operates in a reflection display mode, colored light, which has been transmitted through a portion of a CF other than the opening and reflected by a semi-transmissive reflector, and non-colored light of a high brightness, which has been transmitted through the opening of the CF and reflected by the reflection film, can be output in front of the device, thereby displaying a color image with a high brightness. When the liquid crystal display device operates in a transmission display mode, only colored light, which has been transmitted through the portion of the CF other than the opening, can be output in front of the device, thereby displaying a color image with a high contrast. Note that the publication discloses a pigment dispersion method as a CF formation method (see Paragraph [0040] of the publication).
Japanese Laid-Open Patent Publication No. 8-286178 discloses a reflective or transmissive liquid crystal display device in which a CF including a light-transmitting opening therein is provided for each pixel, and states that it is possible to realize a bright display with the device. The publication also describes the provision of a highly-transmissive CF in a region corresponding to the opening in the CF, and describes methods for forming the highly-transmissive CF, such as a photobleaching reaction of an organic pigment and a partial dying method (see Paragraphs [0103] to [0107] and FIG. 8 of the publication).
Beside the pigment dispersion method, etc., described in the publications above, another CF formation method is a resist direct electrodeposition method as disclosed in, for example, Japanese Laid-Open Patent Publication No. 63-210901. A resist direct electrodeposition method, with which the process can be simplified and which is low in cost, is advantageous over other methods. A process of forming a CF by using a resist direct electrodeposition method will be described with reference to FIG. 24A to FIG. 24J. First, a transparent conductive layer 82 and a positive-type photosensitive resin composition layer 83 are formed in this order on a substrate 81 (FIG. 24A). After a positive-type mask 84 having a predetermined pattern is placed on the photosensitive resin composition layer 83, the structure is exposed, and a portion of the photosensitive resin composition layer 83 in the exposed region thereof is eluted by using an eluent (FIG. 24B). An electric current is passed through the transparent conductive layer 82 in an electrodeposition bath containing an electrodepositing polymer and a dye so as to electrodeposite R (red), for example (FIG. 24C). Other hues, i.e., G (green) and B (blue), are electrodeposited in a manner as that for R (red), thereby forming the photosensitive resin composition layer 83 including colored portions therein (FIG. 24D to FIG. 24G). Then, the entire photosensitive resin composition layer 83 is exposed, and the remaining photosensitive resin composition is eluted in an eluent, thereby leaving the R (red), G (green) and B (blue) color filters on the transparent conductive layer 82. In a case where a CF with no opening (colorless region), as described in Japanese Laid-Open Patent Publication No. 63-210901, is formed, a high patterning precision is not required because it is only necessary to form a CF in each pixel. Note that in an opening in a CF, reflected light is not colored and is substantially colorless. The opening portion of the CF will be referred to also as xe2x80x9ccolorless regionxe2x80x9d.
However, in a case where a CF with an opening therein is formed, a poor patterning precision may result in variations in the area of the opening, leading to variations in the display chromaticity. Therefore, the formation of a CF having an opening therein is stringent as to the patterning precision, making the process control difficult.
With the resist direct electrodeposition method shown in Japanese Laid-Open Patent Publication No. 63-210901, the R, G and B CFs are successively formed by using the same photosensitive resin composition layer 83. Therefore, the sensitivity of the photosensitive resin composition layer 83 gradually decreases, thereby decreasing the CF dimensional precision. Thus, in a case where an opening is formed in a CF by using the resist direct electrodeposition method, the precision in the position or area of the opening decreases along with the decrease in the CF dimensional precision.
In a case where the liquid crystal display device described in Japanese Laid-Open Patent Publication No. 11-183892 is formed by using the resist direct electrodeposition method, variations in the dimension of the CF cause variations in the area of the opening of the CF and, in turn, variations in the display chromaticity.
Japanese Laid-Open Patent Publication No. 8-286178 describes the provision of a highly-transmissive CF in a region corresponding to an opening by using a photobleaching reaction and a partial dying method. Also with these methods, it is necessary to perform a patterning process such as an exposure and development process, thereby causing variations in the area of the opening and, in turn, variations in the display chromaticity. Moreover, a method using the photobleaching reaction has a problem as to the reliability of the obtained CF, i.e., the CF is decolorized in a long-term use. With the partial dying method, a partial dying process needs to be performed for each color, thereby increasing the number of steps.
Moreover, in a case where a CF is formed on a synthetic resin substrate, such a substrate is subject to thermal expansion, which not only changes the dimension but also makes alignment difficult, thereby causing more serious variations in the chromaticity.
An object of the present invention is to provide a reflective or semi-transmissive color liquid crystal display device with a good visibility in which variations in the display chromaticity are reduced. Another object of the present invention is to provide a substrate having colored layers for use in such a liquid crystal display device, and a method for producing the same.
A substrate having colored layers of the present invention includes: a substrate; a reflection layer formed on the substrate; and colored layers of different colors formed on the reflection layer and including a plurality of pixel regions, wherein each of the plurality of pixel regions includes a plurality of colorless regions that are substantially colorless. In the substrate having colored layers of the present invention, a plurality of colorless regions are formed in each pixel, whereby in a reflection display mode, non-colored reflected light is combined with colored reflected light while being dispersed across each pixel. Therefore, bright regions are dispersed across each pixel, thereby reducing the variations in the display chromaticity in each pixel and thus improving the visibility.
Herein, xe2x80x9csubstantially colorlessxe2x80x9d is used to mean not only a hue such that the coloring of the light cannot be visually determined, but also a hue such that the slight coloring of the light for tint adjustment can be visually determined.
It is preferred that a total area of the plurality of colorless regions included in each of the plurality of pixel regions is the same among the colored layers of the same hue. With the substrate having colored layers, the variations in the brightness of non-colored reflected light are reduced among pixels of the same hue, thereby reducing the variations in the display chromaticity among pixels of the same hue and thus improving the visibility.
It is preferred that: a colorless layer that is substantially colorless is formed in each of the colorless regions of the colored layers of different colors; and the colored layers of different colors are formed after the formation of the colorless layers. For example, the colorless layers may be formed by forming a colorless resin film that is substantially colorless and then removing a portion of the colorless resin film in each region other than the colorless regions, and the colored layers of different colors may be formed, one hue after another, in regions other than the regions where the colorless layers have been formed. In the substrate having colored layers, the colored layers of different hues are formed after the size (area) of the colorless region has been determined by the colorless layers, whereby it is possible to obtain a substrate having colored layers including colorless regions of a uniform size (area) independently of the colored layer formation margin.
It is preferred that a flattening film for flattening the colorless layers and the colored layers is formed on the colorless layers and the colored layers, with a refractive index of the colorless layers being substantially the same as that of the flattening film. In the substrate having colored layers, the refractive index of the colorless layer is substantially the same as that of the flattening film, thereby reducing reflection at the interface between the colorless layer and the flattening film and thus improving the optical characteristics.
It is preferred that the colored layers of different colors are red, blue and green colored layers, and as a chromaticity in a reflection mode is measured for each of the hues of the colored layers at a plurality of positions on the substrate, an average value of Y values that are taken for each hue is substantially the same among the plurality of positions on the substrate. In the substrate having colored layers, the average value of Y values that are taken for each hue is substantially the same among different positions on the substrate, whereby a white display by reflected light is uniform across the entire substrate, and thus it is possible to realize a white display as designed.
Each of the plurality of pixel regions may include a transmission region in which light is transmitted and a reflection region in which light is reflected by the reflection layer, with the plurality of colorless regions being included in the reflection region. With the substrate having colored layers, it is possible to obtain a bright display as non-colored reflected light and colored reflected light are combined together under bright environments, whereas it is possible to display a color image by transmitting light from the backlight under dark environments.
The substrate may be a resin substrate.
A production method of the present invention is a method for producing a substrate having colored layers, including a substrate and colored layers of different colors formed on the substrate, the colored layers including a plurality of colorless regions that are substantially colorless, the method including the steps of: forming colorless layers that are substantially colorless on the substrate; and forming the colored layers of different colors, one hue after another, in a region other than the colorless regions in which the colorless layers have been formed. In the production method of the present invention, the colorless layers are formed before the formation of the colored layers, whereby it is possible to reduce the positional shift of the colorless layers as the colorless layers can be formed independently of the precision with which the colored layers are formed. Therefore, it is possible to obtain a substrate having colored layers with reduced variations in the display chromaticity for the same hue among different pixels.
The method for producing a substrate having colored layers of the present invention may include the steps of: forming a resist film on the substrate; exposing and developing the resist film so as to remove a portion of the resist film in each of the colorless regions, and then forming the colorless layers in the colorless regions; and after the formation of the colorless layers, exposing and developing the resist film so as to remove a portion of the resist film in each region where the colored layer is to be formed, and then forming the colored layer. With the production method, it is possible to remove a portion of the resist film in each colorless region through the first exposure and development process, in which the resist sensitivity is highest, whereby it is possible to form a colorless layer in each colorless region with a high precision. Moreover, the resist film used for the formation of the colorless layers can be used also for the formation of the colored layers, thereby simplifying the production process.
In the method for producing a substrate having colored layers of the present invention, it is preferred that the colorless layer is made of the same type of material as a material of the colored layer excluding a pigment. With the production method, it is possible to form the colorless layers by using the same method as that for forming the colored layers, thereby simplifying the production process. Note that xe2x80x9cmaterial of the same typexe2x80x9d refers to a material that is the same as the material of the colored layer excluding the pigment, and the colorless layers are made of a colorless and transparent resin that contains no pigment at all, or a substantially colorless and transparent resin that contains a slight amount of pigment for tint adjustment.
The method for producing a substrate having colored layers of the present invention may include the steps of: forming a photosensitive resin film that is substantially colorless on the substrate; removing a portion of the resin film in a region other than the colorless regions, and forming the colorless layers in the colorless regions; forming the colored layers of different colors, one hue after another, in a region other than the regions in which the colorless layers have been formed. With the production method, it is possible to form the colorless layers in the colorless regions by exposing, developing and sintering the photosensitive resin film. Therefore, it is not necessary to form a resist film on the resin film for the formation of the colorless layers, thereby simplifying the production process.
The method for producing a substrate having colored layers of the present invention may include the steps of: after the formation of the colorless layers, forming a resist film on the substrate; exposing and developing the resist film so as to remove a portion of the resist film in a region where the colored layer of one of the different colors is to be formed, and then forming the colored layer of the one of the different colors; and after the formation of the colored layer of the one of the different colors, exposing and developing the resist film so as to remove a portion of the resist film in a region where the colored layer of another one of the different colors is to be formed, and forming the colored layer of the other one of the different colors. With the production method, it is possible to reduce the positional shift of the colorless layers even in a case where the colored layers are formed by using a successive exposure/development type photoresist, which can be used repeatedly. Therefore, it is possible to obtain a substrate having colored layers with reduced variations in the display chromaticity for the same hue among different pixels.
In the method for producing a substrate having colored layers of the present invention, the colorless layers and/or the colored layers may be formed by electrodeposition. With the production method, even in a case where the colorless layers or the colored layers are formed by using an electrodeposition method such as a resist direct electrodeposition method, variations in the position or area of the colorless regions are unlikely to occur, and thus the variations in the display chromaticity can be reduced.
In the method for producing a substrate having colored layers of the present invention, the substrate may be a resin substrate. With the production method of the present invention, even in a case where a resin (plastic) substrate, which has the problem of thermal expansion, is used, variations in the position or area of the colorless regions are unlikely to occur, and thus the variations in the display chromaticity can be reduced.
A liquid crystal display device of the present invention includes the substrate having colored layers of the present invention. With the liquid crystal display device of the present invention, it is possible to realize a uniform display across the substrate surface with reduced variations in the display chromaticity.
Another liquid crystal display device of the present invention is a liquid crystal display device including a substrate having colored layers that is produced by a method for producing a substrate having colored layers, in which the colorless layers and/or the colored layers are formed by electrodeposition, or by a method for producing a substrate having colored layers, in which the substrate is a resin substrate, wherein it is preferred that a reflection layer is formed on the substrate, the reflection layer including an opening portion that transmits light therethrough and a reflection portion that reflects light, with each of the colorless regions being formed above the reflection portion. The liquid crystal display device is a semi-transmissive color liquid crystal display device, and the substrate having colored layers used therein is such that the colorless regions are formed in the colored layer with a high precision, and each colorless region of the colored layer is formed above the reflection portion of the reflection layer without a positional shift. Therefore, it is possible to realize a uniform display across the substrate surface with reduced variations in the display chromaticity.
The liquid crystal display device of the present invention has a very wide variety of applications, and can be used in an electronic device of any field. The liquid crystal display device of the present invention is capable of displaying a color image with a high quality both in a reflection mode and in a transmission mode, and it is thus highly suitable for portable electronic devices that are used under considerably different environments and that are required to have a low power consumption, e.g., portable electronic devices that are used while being moved between an outdoor environment and an indoor environment. Moreover, other applications include a bulletin board system, a facsimile machine, and a display of a home electronics terminal.